To follow up then,

I have assumed that dfdl:emptyValueDelimiterPolicy isn't even examined unless the element has default="..." i.e., a non-zero-length default value specified. I.e., without a default value, there is no concept of emptiness as distinct from "normal" representation.

Are you suggesting that it is also used to control when an empty string (or empty hexbinary) is accepted as a normal representation value for an optional element, vs. treated as a missing value? That's a reasonable interpretation that I would support, but I don't know that the spec says that anywhere, so we need to add a sentence. (Unless I'm missing where this is stated.)

I have also thought that dfdl:emptyValueDelimiterPolicy must be combined with dfdl:initiator and dfdl:terminator. If the combination of these is such that the empty representation is zero-length, that is what creates the situation of interest here, where it is ambiguous whether the value is the official empty representation or is the normal representation that just so happens to be of zero length. That is, there's no special significance to the 'none' EVDP property value.

For example, if dfdl:emptyValueDelimiterPolicy is 'both', but dfdl:initiator="" and dfdl:terminator="", then that's just as good as dfdl:emptyValueDelimiterPolicy='none' in terms of whatever effect this has on a decision about normal vs. missing.

Does this match your understanding?

Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com

Please note: Contributions to the DFDL Workgroup's email discussions are subject to the OGF Intellectual Property Policy

On Wed, Aug 1, 2018 at 9:26 AM, Steve Hanson <smh@uk.ibm.com> wrote:

Whether to add a zero-length string or hexBinary to the infoset for an optional element depends on the setting of emptyValueDelimiterPolicy. A setting of 'none' stops it from being added.

Regardless, it does not give a processing error, so is therefore known-to-exist, and therefore does not cause backtracking, so preserving discriminators and variables.

Regards

Steve Hanson
IBM Hybrid Integration, Hursley, UK
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
smh@uk.ibm.com
tel:+44-1962-815848
mob:+44-7717-378890
Note: I work Tuesday to Friday

From: Mike Beckerle <mbeckerle.dfdl@gmail.com>
To: dfdl-wg@ogf.org
Date: 24/07/2018 15:15
Subject: [DFDL-WG] clarification: on suppressed ZL string/hexBinary - do we keep variable assignments?
Sent by: "dfdl-wg" <dfdl-wg-bounces@ogf.org>

In some situations we parse and get a successful zero-length parse for a string or hexBinary.

But because the occurrence is optional, we do NOT add an element to the infoset.

In that case, what happens to side-effects that occurred during the successful parse. There are two possible kinds of side-effects. Variables can be set, and a discriminator can be set to true.

It seems to me that if a discriminator is set, then that *must* be preserved, and in that case it would seem the variable settings should be retained as well.

Comments?

Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com
Please note: Contributions to the DFDL Workgroup's email discussions are subject to the OGF Intellectual Property Policy
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